Portable electronic devices such as mobile phones, media players, smart phones, and the like often provide “silent alerts” that are designed to catch a user's attention without providing an audible signal from a speaker. Frequently, the silent alert is set by the user when an audible alert would be disruptive, such as in a meeting or a theater, for example. The silent alert allows for the user to receive notification of some event, such as in incoming call or text, for example, discretely. Some users may even use the silent alert as their default notification mechanism.
Typically, the silent alert is provided by a haptic device, such as a vibrating device, intended to allow the user to feel the activation of the alert. There are two common vibrating devices that are currently implemented. One includes an eccentric weight coupled to a motor driven shaft that, when rotated, provides vibration. Another includes a linear vibrator that rather than having rotational movement, displaces in a linear path. The two types of vibrators present separate issues.
With regard to the rotating eccentric weight vibrator, the silent alerts are not so silent in some instances. Specifically, for example, when a mobile phone is set to actuate a silent alert while it is in contact with a hard surface (e.g., on a table or a shelf, or in a drawer), the rotating eccentric weight may cause the mobile phone to vibrate and rattle against the surface. In some cases, the noise caused by the rattling exceeds that of audible alerts and may be much more disruptive. Further, the mobile phone may move along the surface when the vibrating device is activated, thus placing the mobile phone at risk of falling.
The linear vibrator may similarly exhibit some of the same symptoms as the rotating eccentric weight vibrators, but perhaps not to the same degree. The mechanical structure of the linear vibrators may also result in their weights being displace when not actuated. In particular, when moved in or impacted in a direction that corresponds to the direction of linear displacement of the linear vibrator, displacement of the weight may occur and a user may sense the displacement. In some cases, the sensed displacement may feel spongy and/or detract from a user's impression of quality of the device in which the linear vibrator is implemented.